Vasodilators are medicines that open, also called dilate, blood vessels. Vasodilators affect the muscles in the walls of the arteries and veins. They prevent the muscles from tightening and the walls from narrowing.

As a result, blood flows more easily through the vessels. The heart doesn't have to pump as hard. This reduces blood pressure.

The vasodilators that work directly on the vessel walls are hydralazine and minoxidil. Some other medicines used to treat high blood pressure, such as calcium channel blockers, also dilate blood vessels.

Vasodilators are prescribed to prevent, treat or improve symptoms in many conditions, such as:

• High blood pressure.
• High blood pressure during pregnancy or childbirth.
• Heart failure.
• High blood pressure that affects the arteries in the lungs, called pulmonary hypertension.

Direct vasodilators are strong medicines that generally are used only when other medicines haven't controlled blood pressure well enough.

These medicines have a number of side effects. Some side effects may need to be treated by taking other medicines.

Side effects include:

• Fast heartbeat.
• Fluttering, pounding or rapid heartbeat, called palpitations.
• Swelling due to fluid buildup in the body, called edema.
• Nausea.
• Vomiting.
• Headache.
• Excessive hair growth.
• Joint pain.
• Chest pain.

Talk to your health care team if you have any questions about the medicines you take.